1. Field of the Invention
This invention relates to film thickness detector systems and more particularly to such systems which detect a splice or other abnormality on the surface of a film longer than a desired length.
2. Description of the Prior Art
It is known to provide a sensing arm biased against the surface of a film to detect film thickness changes. When an abnormal splice passes under the sensing arm a switching curcuit is activated to stop the travel of the film.
In U.S. Pat. No. 3,778,802, splices longer than a predetermined length are sensed by a single feeler arm which cooperates with a timing circuit which senses the beginning and end of the splice. If the time between the beginning and end of the sensed splice is longer than the time established within the circuitry, then the film travel is stopped. Such a system has the disadvantage of using a mechanical sensing arm. Furthermore, in the system of U.S. Pat. No. 3,778,802 an additional timing circuit is required.